1. Field of the Invention
The present invention relates to modulators and demodulators and, more particularly, to a method and apparatus for switching between multiple waveforms.
2. Description of Related Art
In recent years due to the rapid development of multimedia, digital, audio, and video communications applications, there is a necessity for efficient and reliable signal modulation and demodulation techniques to accommodate different modulation formats based on the media over which the signals are to be transmitted. For instance, with respect to high definition television, and in fact other types of advanced television transmissions, program material in video, data, or audio form is formatted by a channel encoder to be transmittable by Vestigial Side Band modulation or VSB which is typical for over-the-air television transmissions. Quadrature Amplitude Modulation or QAM is typically used for cable transmissions, whereas Quadrature Phase Shift Keying or QPSK is generally used in satellite communication. For radio communications Time-Division Multiplexing (TDM) modulation and error correction formats are utilized. Finally, discrete multitone or DMT techniques are typically used for telephone landline signaling such as with Asymmetric Digital Subscriber Lines or ADSL. It will be appreciated that when a video source at the transmit side is encoded through a source coding unit, the source coding unit is set up to code the video source material in one of the four above-mentioned modulation formats. Likewise, on the receive side in order for a receiver to decode all of the above mentioned formats discrete VLSI chips or detectors can be provided in parallel, with the outputs going to source decoding.
It is apparent that receivers utilized for processing multiple modulation formats utilize a series of demodulators each configured to demodulate a particular format. This duplication of demodulators is costly and may suffer technical problems such as switching transients and cross modulation between different demodulators.
Furthermore, in a radio (modem) application, where characteristics such as modulation type, data rate, error correction coding, etc, are required to change quickly during operation, prior art methods of processing multiple-modulation formats can result in loss of data and dataflow.
It will be thus appreciated that any parallel processing solution to the problem of multiple modulation formats generally involves increased hardware complexity and increased cost.
It is therefore an object of the present invention to provide a receiver capable of demodulating multiple modulation formats without losing data or interrupting dataflow, the receiver containing a single demodulator with re-configurable logic therein.
It is a further object of the present invention to provide a method for demodulating multiple waveforms of different characteristics, in a software defined demodulator, without losing data or interrupting dataflow.
It is still a further object of subject invention to demodulate multiple waveforms in the same hardware by providing a re-configurable software defined demodulator that reconfigures itself in response to varying input waveform configuration parameters.